Embryos grow autonomously during preimplantation development, and the, upon implantation, both maternal and embryonic cells proliferate and differentiate into specialized tissues. There is little information about what growth factors are present in implanting embryos and what role they play in information transfer in the embryo itself and between embryo and mother. The aim of this project is to identify and characterize the role of growth factors functioning at the level of both embryo and maternal tissue during this peri-implantation period. To test the hypothesis that these growth factors and/or their receptors function in growth and differentiation in the peri-implantation period it is essential to derive qualitative and quantitative data on their expression. The approach will use RT-PCR for initial identification of transcripts from the growth factor and receptor genes, followed by analysis of expression of the protein products of these genes by immunologic means. Once expression of some growth factors and their receptors in the peri-implantation embryo have been defined, the function of these receptors and ligands within the embryo or between embryo and mother will be studied with blocking or antagonistic antibodies or binding proteins added to embryos. Another approach will involve addition of purified or recombinant growth factors or agonistic antibodies to peri-implantation embryos to see if these stimulate embryonic growth or affect genes downstream from the growth factor action (e.g., c- fos). Undifferentiated and differentiated embryonic stem cells will also be studied for growth factor production. Ultimately, the definitive determination of the function of a specific gene can be made only by deleting the function of that gene phenotypically. The genes for growth factors and their receptors present a particular challenge because there is an apparent overlap in the functions of several ligands and receptors, which may be expressed at the same time. Antisense RNA or DNA will be introduced into embryos with sense constructs as controls, and cell proliferation monitored. Another approach to abrogate genes is by homologous recombination to delete functional genes. Homologous recombinant embryonic stem cell lines will be selected and transferred into embryos for germ line transmission. These experiments should lead to a better understanding of early embryonic growth and differentiation around the time of implantation. Because abnormal early growth and implantation are a major source of embryo wastage, the experiments may provide a basis for improving successful pregnancy after in vitro fertilization.